Evidence from Caustic Waveform Modeling for Long Slab Thickening above the 660-km Discontinuity under Northeast Asia: Dynamic Implications

This chapter presents a study that aims at constraining the thickness of the slab in the mantle transition zone beneath northeast Asia through the method of caustic waveform modeling for both P and S waves. It discusses the author's finding of a thickened slab in the upper mantle transition zone beneath northeast Asia and the possible mechanism of its formation. The chapter first shows the sensitivity of the method to the structure around the 660-km discontinuity, and then briefly introduces the data sources and main features of the resolved P and S velocity models. It argues that the thickening of the slab due to buckling instability may partly explain the enigma of the missing Pacific slab. The chapter speculates that such a thickened stagnant slab might be close to an impending instability with a rapid flush of cold material possibly occurring in the next few million years.